1. Field of the Invention
The present invention relates generally to developing devices and image forming apparatuses.
2. Description of the Related Art
Conventionally, developing devices configured to convey externally-supplied developer to a developer bearer through a developer conveyance path while discharging surplus developer in the developer conveyance path via a developer discharge port by causing an overflow are known.
An example of such a developing device is disclosed in Japanese Patent No. 5158473. The developing device disclosed in Patent Document 1 obtains a toner image by developing an electrostatic latent image borne on a photoconductor, which is a latent image bearer, with developer containing toner and magnetic carrier particles and borne on a surface of a developing roller, which is a developer bearer. The developer, the toner of which is consumed in the development, is released from the surface of the developing roller, collected into a recovery conveyance path, and conveyed by rotation of a recovery screw in an axial direction of the screw. Thereafter, the developer conveyed to a downstream end of the recovery conveyance path is pushed up to a feeding conveyance path arranged above the recovery conveyance path and conveyed in the direction opposite to the conveying direction of the recovery screw by rotation of a feeding screw. During this conveyance, the developer is fed to the developing roller arranged parallel to the feeding screw. Developer conveyed to a downstream end of the feeding conveyance path without being fed to the developing roller is let fall to an upstream end of the recovery conveyance path. At this time, surplus developer is discharged through a developer discharge port by overflow. The surplus developer is produced because, when concentration of toner declines as toner is consumed in development, fresh toner is replenished to the recovery conveyance path. If flowability of toner in the developer drops due to an environmental change or the like, it is possible that the developer is not overflown through the developer discharge port favorably, causing an amount of the developer in the developing device to become excessive. To avoid this, a loosening screw for mechanically loosening the developer is arranged above the feeding screw at a same level as the developer discharge port. According to Japanese Patent No. 5158473, it is possible to cause the developer to be overflown through the developer discharge port smoothly by mechanically loosening the developer by rotating the loosening screw.
However, the above-described configuration is disadvantageous in that, because the loosening screw, which rotates by being driven, is used as a loosening member for mechanically loosening the developer, a dedicated drive mechanism for driving the loosening screw is required, which leads to an increase in cost.